This project is designed to use nucleic acid hybridization techniques to analyze human cancer cells for the presence of nucleic acids related to RNA genomes of selected mammalian retroviruses. As part of this overall goal, we have found that rat cells producing Moloney murine sarcoma virus contain intracelular, virus-specific RNA which is complementary in base sequence to the RNA genome of the Molony virus and represents a minimal 74% of the RNA genome. A measurement of the copy number of this viral complementary RNA relative to that of viral genomic RNA has disclosed 14 copies of complementary RNA per cell and 1,272 copies of genomic RNA per cell. In another related study, we have observed that Kirsten murine sarcoma virus has two subunit RNA's. One subunit RNA has a sedimentation coefficient of 275 and an estimated molecular weight of 2.0 X 10 to the 6th power daltons. The second subunit RNA has a sedimentation coefficient of 31S and a molecular weight estimate of 2.5 X 10 to the 6th power daltons. An examination of their nucleotide sequence compositions as determined by cross-hybridization with complementary DNA transcripts of Gross murine leukemia virus and a rat endogenous retrovirus released from Wistar rat cells has revealed that the MSV-K 27S subunit RNA representing 5.9 kilobases consists of Gross virus sequences (36%), rat endogenous virus sequences (30%) and unidentified sequences (34%) which presumably are rat cellular genetic elements. In contrast, the MSV-K 31S subunit RNA representing 7.4 kilobases consists of more Gross virus sequences (72%), less rat endogenous sequences (8%), and unidentified sequences (20%) which are also probably rat cellular genetic elements.